1. Technical Field
This application relates generally to the field of power delivery systems.
2. Description of the Related Art
In recent years, circuits for medium-voltage variable frequency drive (VFD) applications have received attention. Several novel methods have been introduced in the past decade. For example, in a circuit comprising series-connected inverters as described in U.S. Pat. No. 5,625,545 to Hammond, the disclosure of which is incorporated herein by reference in its entirety, an inverter or power cell 110 includes a three-phase diode-bridge rectifier 112, one or more direct current (DC) capacitors 114, and an H-bridge inverter 116. The rectifier 112 converts the input 118 alternating current (AC) voltage to a substantially constant DC voltage that is supported by the capacitors 114 that are connected across the rectifier 112 output. The output stage of the inverter 110 includes an H-bridge inverter 116 that includes two poles, a left pole and a right pole, each with two devices. The inverter 110 transforms the DC voltage across the DC capacitors 114 to an AC output 120 using pulse-width modulation (PWM) of the semiconductor devices in the H-bridge inverter 116.
Other circuits and drives for medium voltage and high voltage motor control are available. In general medium voltage refers to a rated voltage greater than 690 volts (V) and less than 69 kilovolts (kV). In some embodiments, medium voltage may be a voltage between about 1000 V and about 69 kV. High voltage ratings exceed such medium voltage ratings. In many such systems, modular power cells are used. Industry often seeks ways to reduce the size of such systems, increase the life and reliability of the systems, and permit the systems to keep operating under on or more fault conditions.
The disclosure contained herein describes attempts to solve one or more of the problems described above.